Added locking primitive lazy_mutex, which has essentially the same behaviour

as a mutex, but allocates its semaphore lazily. This comes at the cost of an
additional atomic_add() when the semaphore has actually to be acquired, but
saves the semaphore creation completely in single-threaded programs and in
any program when there's no lock contention.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34339 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/shared/locks.h

@@ -22,6 +22,19 @@ status_t	mutex_lock(mutex *lock);
 void		mutex_unlock(mutex *lock);
 
 
+typedef struct lazy_mutex {
+	int32		benaphore;
+	sem_id		semaphore;
+	const char*	name;
+} lazy_mutex;
+
+status_t	lazy_mutex_init(lazy_mutex *lock, const char *name);
+				// name will not be cloned and must rename valid
+void		lazy_mutex_destroy(mutex *lock);
+status_t	lazy_mutex_lock(lazy_mutex *lock);
+void		lazy_mutex_unlock(lazy_mutex *lock);
+
+
 typedef struct rw_lock {
 	const char *			name;
 	mutex					lock;